Prior Art
The present invention relates to a method for drilling a processed hole to a hard but brittle material and a device for carrying out the method. A diamond core drill (1) is, as shown in FIG. 3, a device having for a diamond whetstone part (2) which is mounted on the top end of a steel shank (3) for drilling a hole to a material to be processed. In general the diamond core drill is provided with a penetrating part (4) at the central portion of a drill.
The diamond core drill is excellent both in processing efficiency and processing accuracy for drilling a hole to a hard and brittle material, however, there has been a fault to generate breaking-offs at an opening edge of the drilled hole.
The breaking-offs impair not only accuracy and beautiful appearance, but also are apt to cause cracks to break materials such as plate glasses etc.
Breaking-offs are generated at the side of a material to be drilled from which the diamond core drill falls out, when the drill penetrates the material, such as a plate glass, to be drilled. Therefore, in order to prevent breaking-offs, in conventional, one of the methods for drilling a hard but brittle material especially such as a plate glass or the like, drilling operation is carried out from both sides thereof in which at first the drilling operation is begun from one side of the plate glass and continued till depth of a hole drilled therein reaches to about a half of thickness of the plate glass, and then, the drilling operation is carried out from a oppositely corresponding position of the other side of the plate glass that a hole drilled from the other side thereof may communicate with the firstly drilled hole to complete a penetrating hole at their meeting part, that is, about at the center of the plate glass thickness.
However, in the afore-described conventional method of drilling material such as plate glass or the like from the both sides thereof, two spindles must be disposed to exactly oppose with each other in keeping coaxial relation, however, accurate coaxial relation between the two spindles is not always achieved which results in difference at the meeting point of the two holes.
Further, in this conventional method though no breaking-off is generated at the opening part of the hole, there generate several causes to lead crackings at the penetrated part, that is, at the meeting part of the two holes. To solve the afore-described disadvantage other method has been proposed in which drills having somewhat different diameters are used at both sides, respectively. However, in this method there is also disadvantage to occur a stepped portion in the hole.
The present invention is aimed to solve the afore-described disadvantages of the conventional methods. According to the present invention, a penetrating hole can be drilled to a hard but brittle material such as plate glass or the like without generating any breaking-offs by using a single diamond core drill from one side of the material to be drilled.